I'm a well read grad student who's bluntly honest about all things, although I try to be most honest about myself.
You can't. Sighs. Well, the most important are the TF books and I have MTMtE and RiD via Humble Bundle. So, I'm not crushed or anything. If I really want them in paperback, I'll buy them again. Or even get them on sale via Comixology if I can't bring myself to buy them physically and lose access to HB.
I'm curious: what do you do? I either don't give books out or give them to, say, family members where I'll know I"ll get them back or don't feel so bad asking for them back.